1. Field of the Invention
The present invention is generally related to a Hall effect element and, more particularly, to a vertical Hall effect element for measuring the strength of magnetic fields within an epitaxial layer of a silicon device in which the contact diffusion regions of the Hall effect element are shaped and sized by the configuration and size of openings formed in a position diffusion which is provided specifically for the purpose of defining the position of the contact diffusions of a different conductivity type than the contact diffusions.
2. Description of the Prior Art
The Hall effect has been known for many years. One of the first practical applications of the Hall effect was as a microwave power sensor in the 1950's. With the later development of the semiconductor industry and its increased ability for mass production, it became feasible to use Hall effect components in high volume products. In 1968, Honeywell's MICRO SWITCH division produced a solid state keyboard using the Hall effect. The Hall effect sensing element and its associated electronic circuit are often combined in a single integrated circuit.
In its simplest form, the Hall element is constructed from a thin sheet of conductive material with output connections perpendicular to the direction of electrical current flow. When subjected to a magnetic field, the Hall effect element responds with an output voltage that is proportional to the magnetic field strength. The combination of a Hall effect element in association with its associated signal conditioning and amplifying electronics is sometimes called a Hall effect transducer.
A comprehensive source of information about Hall effect devices is provided in a book by R. S. Popovic which is titled "Hall Effect Devices: Magnetic Sensors and Characterization of Semiconductors" which was published under the Adam Hilger Imprint by IOP Publishing Limited. On page 3 of the Popovic book, a horizontal Hall device is shown in the form of a rectangular plate. Modern Hall element plates are usually manufactured with microscopic dimensions. As an example, the book written by Popovic describes a Hall effect element that has a thickness of approximately 10 micrometers, a length of approximately 200 micrometers and a width of approximately 100 micrometers. When this type of configuration is used for the measurement of a magnetic field which extends perpendicularly through the thickness of the Hall element, it is common to refer to the device as a horizontal Hall element. If, on the other hand, a Hall element is constructed for the purpose of measuring the magnitude of a magnetic field extending in parallel within the plane of a conductor, it is common to refer to the device as a vertical Hall element. The concept of a vertical Hall element is described in the Popovic reference and illustrated in FIG. 5.7 on page 203.
In both horizontal and vertical Hall elements, the output signal from the Hall element is representative of the magnitude of the magnetic field which is perpendicular to the sensing plane of the Hall effect element and perpendicular to the direction of current flow through the Hall element. This principle is well known to those skilled in the art and is true for both horizontal and vertical Hall elements.
When provided in silicon, a horizontal Hall element is typically provided within the epitaxial layer which, in turn, is disposed on a silicon substrate structure. Appropriate current providing contacts and voltage sensing contacts are disposed on the semiconductor and the Hall effect element provides an output signal that is responsive to the magnitude of the magnetic field extending perpendicular to the surface of the epitaxial layer. A vertical Hall effect element manufactured in silicon, on the other hand, is intended to measure the magnitude of a magnetic field extending within the epitaxial layer and parallel to the surface of the epitaxial layer. If the vertical Hall element is considered as being analogous to a horizontal Hall effect element standing on its edge, the height of the Hall effect element is limited to the thickness of the epitaxial layer whereas the thickness of the epitaxial layer merely limits the thickness of the Hall effect plate in a horizontal Hall element. Therefore, the accurate sizing and location of the electrical contacts must be much more precise in vertical Hall elements than in horizontal Hall elements. Since the normal tolerances that are available in typical semiconductor masking operations do not normally provide the necessary accuracy to produce a vertical Hall effect element which has relatively high sensitivity, it would be significantly beneficial if these normal semiconductor masking procedures could be adapted in such a way that the highly accurate positioning and sizing of the contacts for a Hall effect element could be provided.